wasmtime 40.0.0

//! Support for a calling of an imported function.

use crate::prelude::*;
use crate::runtime::vm::{
    Instance, StoreBox, VMArrayCallHostFuncContext, VMContext, VMOpaqueContext, VMStore,
};
use crate::store::InstanceId;
use crate::type_registry::RegisteredType;
use crate::{FuncType, ValRaw};
use core::ptr::NonNull;

struct TrampolineState<F> {
    func: F,

    // Need to keep our `VMSharedTypeIndex` registered in the engine.
    _sig: RegisteredType,
}

/// Shim to call a host-defined function that uses the array calling convention.
///
/// Together with `VMArrayCallHostFuncContext`, this implements the transition
/// from a raw, non-closure function pointer to a Rust closure that associates
/// data and function together.
///
/// Also shepherds panics and traps across Wasm.
///
/// # Safety
///
/// Requires that all parameters are valid from a wasm function call and
/// additionally that `vmctx` is backed by `VMArrayCallHostFuncContext`.
unsafe extern "C" fn array_call_shim<F>(
    vmctx: NonNull<VMOpaqueContext>,
    caller_vmctx: NonNull<VMContext>,
    values_vec: NonNull<ValRaw>,
    values_vec_len: usize,
) -> bool
where
    F: Fn(&mut dyn VMStore, InstanceId, &mut [ValRaw]) -> Result<()> + 'static,
{
    // SAFETY: this is an entrypoint of wasm calling a host and our parameters
    // should reflect that making `enter_host_from_wasm` suitable. Further
    // unsafe operations are commented below.
    unsafe {
        Instance::enter_host_from_wasm(caller_vmctx, |store, instance| {
            // SAFETY: this function itself requires that the `vmctx` is valid to
            // use here.
            let state = {
                let vmctx = VMArrayCallHostFuncContext::from_opaque(vmctx);
                vmctx.as_ref().host_state()
            };

            // Double-check ourselves in debug mode, but we control
            // the `Any` here so an unsafe downcast should also
            // work.
            //
            // SAFETY: this function is only usable with `TrampolineState<F>`.
            let state = {
                debug_assert!(state.is::<TrampolineState<F>>());
                &*(state as *const _ as *const TrampolineState<F>)
            };
            let mut values_vec = NonNull::slice_from_raw_parts(values_vec, values_vec_len);
            // SAFETY: it's a contract of this function itself that the values
            // provided are valid to view as a slice.
            let values_vec = values_vec.as_mut();
            (state.func)(store, instance, values_vec)
        })
    }
}

pub fn create_array_call_function<F>(
    ft: &FuncType,
    func: F,
) -> Result<StoreBox<VMArrayCallHostFuncContext>>
where
    F: Fn(&mut dyn VMStore, InstanceId, &mut [ValRaw]) -> Result<()> + Send + Sync + 'static,
{
    let array_call = array_call_shim::<F>;

    let sig = ft.clone().into_registered_type();

    unsafe {
        Ok(VMArrayCallHostFuncContext::new(
            array_call,
            sig.index(),
            Box::new(TrampolineState { func, _sig: sig }),
        ))
    }
}